A man is caught leaving a Daly City grocery store with two frozen pizzas and several candy bars he didn't pay for.

Employees at the Lucky's on Mission Street recognize him as the same quiet and weary-looking man who tried to steal those same items twice before.

They alert the authorities, and he is placed under arrest. He goes with them calmly, in tattered clothing that led officers to write in the police report that he looked like he had been living on the streets.

As they process him - taking his fingerprints and mug shot and bringing him to his cell in San Mateo County jail - he doesn't make a single peep.

Nearly a month later, he still hasn't - and investigators said they have no idea who he is.

Since Daly City police arrested the man May 30, he hasn't once opened his mouth to speak, nor has he responded to other attempts to get him to communicate.

The man had no identification on him, and fingerprint scans through state and criminal databases haven't turned up any results, said Rich Fischer, an investigator who works with the county private defender's office.

Doctors found nothing wrong with his vocal cords, and psychologists are having difficulty making a diagnosis without being able to communicate with him, Fischer said.

But the man responds to simple commands such as, "Raise your arms," given in either English or Tagalog, a language spoken in the Philippines, Fischer said. He does not maintain eye contact with the person trying to engage him.

"When I would sit next to him, I'd give him a tablet and a pen and I'd ask him, 'Can you write some letters?' No response," Fischer said.

The man is being held in a mental health unit, Fischer said. Investigators will flood the Daly City neighborhood this weekend where the man was arrested to look for leads.

Despite the strange circumstances, the man does not seem distressed or pained about his situation, Fischer said. In fact, in the one breakthrough investigators had with him, he seemed to be saying he was fine.

"In response to a nurse's question asking, 'Are you happy or are you sad?' he drew a happy face," Fischer said. "That is the only response anyone has gotten from him."